Chapter 21
Production Geology
Knut Bjørlykke
Production Geology has become an important field
and in mature sedimentary basins more geologists
and geophysicists are involved in production than
exploration. Today more of the global reserves of
petroleum are added by increasing the recovery in
existing fields than by discovering new fields.
The development of horizontal drilling has made it
possible to produce oil much more efficiently than
from vertical wells. It is now possible to drill wells
up to 8–9 km along a very complex path draining
several small reservoir compartments. Horizontal drilling has also opened up for production from low permeability reservoirs and from shales. See Chap. 23 on
unconventional oil and gas.
During high oil prices much more can be invested
in methods to increase oil and gas recovery.
The production of oil and gas requires detailed
mapping of the reservoir with respect both to the
distribution of petroleum and the flow properties of
the reservoir rock.
After the discovery of a new field it may therefore
be necessary to drill some delineation wells to acquire
more information about the extent of the reservoir and
the distribution of reservoir properties. Production
wells and injection wells must be planned carefully
to secure optimal recovery. Each new production well
will provide a large database which needs to be
interpreted; this will include information about pressure barriers in the reservoir. In many cases 3D seismic surveys will be repeated during the producing
lifetime of the reservoir, providing a fourth dimension
(time) to make it a 4D survey, see Chap. 19. It is then
often possible to follow the change in the oil/water
contact, gas/oil contact or gas/water contact by the
density and velocity contrast which is a function of
petroleum saturation. This may enable poorly drained
parts of the reservoir to be identified and the financial
feasibility of drilling a new production well to drain
this part to be assessed.
Securing optimal production from oil and gas fields
is an important challenge both from an economical
and environmental perspective. The presence of free
gas provides good pressure support for the oil production. The oil must normally be produced before the
gas, otherwise production of the gas will reduce the
reservoir pressure markedly and distort the oil/gas
contact, making it difficult to recover the remaining
oil. There is also gas dissolved in the oil and water
which will bubble up from the oil phase and the water
phase when the pressure is reduced during production.
(Fig. 21.1).
21.1 Capillary Forces
The pores in the reservoir rocks may be filled with oil
and water and in some cases there may be also gas so
that we have three phases. This complicates and
retards fluid flow in the reservoir during production.
The contact between the solid phase, mostly minerals
and the fluid phases is then very important. Minerals
have different preferences to be wetted by fluids such
as water, oil and gas. This is measured by the wetting
angle which depends on temperature, pressure and the
composition of the fluids.
K. Bjørlykke (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_21, # Springer-Verlag Berlin Heidelberg 2015
545
Production Geology
Knut Bjørlykke
Production Geology has become an important field
and in mature sedimentary basins more geologists
and geophysicists are involved in production than
exploration. Today more of the global reserves of
petroleum are added by increasing the recovery in
existing fields than by discovering new fields.
The development of horizontal drilling has made it
possible to produce oil much more efficiently than
from vertical wells. It is now possible to drill wells
up to 8–9 km along a very complex path draining
several small reservoir compartments. Horizontal drilling has also opened up for production from low permeability reservoirs and from shales. See Chap. 23 on
unconventional oil and gas.
During high oil prices much more can be invested
in methods to increase oil and gas recovery.
The production of oil and gas requires detailed
mapping of the reservoir with respect both to the
distribution of petroleum and the flow properties of
the reservoir rock.
After the discovery of a new field it may therefore
be necessary to drill some delineation wells to acquire
more information about the extent of the reservoir and
the distribution of reservoir properties. Production
wells and injection wells must be planned carefully
to secure optimal recovery. Each new production well
will provide a large database which needs to be
interpreted; this will include information about pressure barriers in the reservoir. In many cases 3D seismic surveys will be repeated during the producing
lifetime of the reservoir, providing a fourth dimension
(time) to make it a 4D survey, see Chap. 19. It is then
often possible to follow the change in the oil/water
contact, gas/oil contact or gas/water contact by the
density and velocity contrast which is a function of
petroleum saturation. This may enable poorly drained
parts of the reservoir to be identified and the financial
feasibility of drilling a new production well to drain
this part to be assessed.
Securing optimal production from oil and gas fields
is an important challenge both from an economical
and environmental perspective. The presence of free
gas provides good pressure support for the oil production. The oil must normally be produced before the
gas, otherwise production of the gas will reduce the
reservoir pressure markedly and distort the oil/gas
contact, making it difficult to recover the remaining
oil. There is also gas dissolved in the oil and water
which will bubble up from the oil phase and the water
phase when the pressure is reduced during production.
(Fig. 21.1).
21.1 Capillary Forces
The pores in the reservoir rocks may be filled with oil
and water and in some cases there may be also gas so
that we have three phases. This complicates and
retards fluid flow in the reservoir during production.
The contact between the solid phase, mostly minerals
and the fluid phases is then very important. Minerals
have different preferences to be wetted by fluids such
as water, oil and gas. This is measured by the wetting
angle which depends on temperature, pressure and the
composition of the fluids.
K. Bjørlykke (*)
Department of Geosciences, University of Oslo, Oslo, Norway
e-mail: knut.bjorlykke@geo.uio.no
K. Bjørlykke (ed.), Petroleum Geoscience: From Sedimentary Environments to Rock Physics,
DOI 10.1007/978-3-642-34132-8_21, # Springer-Verlag Berlin Heidelberg 2015
545